Method of producing cubic boron nitride coated material

ABSTRACT

There are disclosed a cubic boron nitride coated material including a substrate and an outer layer composed principally of cubic boron nitride and formed on a surface of the substrate, comprising an intermediate layer fored of at least one intermediate layer and interposed between the substrate and outer layer, the intermediate between the substrate and outer layer, the intermediate layer or the outermost one of intermediate layers being formed of a layer of at least one nitrogen-containing compound selected from the nitrides and nitroxides of Al, Ga, In and Tl and mutual solid solutions thereof, and a producing method of the same which comprises:  providing, on the surface of the substrate, an intermediate layer formed of at least one intermediate layer, the intermediate layer or the outermost one of intermediate layers being formed of a layer of at least one nitrogen-containing compound selected from the group consisting of nitrides and nitroxides of Al, Ga, In and Tl and mutual solid solutions thereof; and  causing the outer layer to undergo oriented growth on a face of the layer of the at least one nitrogen-containing compound, the face being densely packed with nitrogen atoms.

This is a division of application Ser. No. 886,068, filed July 16, 1986,U.S. Pat. No. 4,731,303.

BACKGROUND OF THE INVENTION

This invention relates to cubic boron nitride coated material useful asa tool, such as a cutting tool, a wear resistant tool and the like andan electronic part such as a semiconductor substrate and the like, andthe producing method thereof.

Roughly classifying, boron nitride (BN) is present in two types offorms, one being low-density boron nitride and the other high-densityboron nitride. Of these, as a representative example of high-densityboron nitride, there is cubic boron nitride which is synthesized underspecial conditions such as high-pressure and high-temperature.

Cubic boron nitride has high hardness, high heat conductivity and highelectric insulating property, second to diamond, and moreover, enjoyschemical stability, oxidation resistance, heat resistance and thermalshock resistance all better than diamond. While diamond has highaffinity with Iron-group metals, cubic boron nitride has low affinitywith them. Therefore, cubic boron nitride is paid attention, forexample, as a material for tools used for cutting or grinding Iron-groupmetal materials. In spite of such excellent properties as mentionedabove, cubic boron nitride is brittle and has low sinterability andlimitations are hence imposed on its shape and applicaiton.

Thus, it has been attempted to form cubic boron nitride as a coatinglayer on a surface of a substrate in order to solve the above-mentionedlimitations to the shape and application.

Formation of coating layers of boron nitride can generally be carriedout, roughly speaking, by chemical vapor deposition method (CVD method),physical depostion method (PVD method) and plasma-assisted CVD method(PCVD method). Of these, CVD method is effected by using, asillustrative, reactant gases comprising a boride such as a boronhalogenide or diborane, hydrogen, and ammonia or hydrazine. PVD methodincludes, for example, the ion beam deposition method, ion injectionmethod, sputtering method and ion plating method as well as combinationsof the ion injection method with other PVD methods. In plasma-assistedCVD method, a coating layer of boron nitride is synthesized in a vaporphase in the stream of plasma. As a prior art publication disclosingtools obtained by forming coating layers actually consisting of cubicboron nitride on substrates, Japanese Provisional patent publication No.95881/1982 has been known.

Among conventional methods for forming coating layers consisting ofboron nitride, CVD method is accompanied by a problem that coatinglayers comprising of hexagonal boron nitride or amorphous boron nitridecan only be formed because it is a mere thermal vapor-phase synthesis.On the other hand, when PVD method or plasma-assisted CVD method isrelied upon, a coating layer composed of boron nitride having arelatively high hardness is formed. Cubic boron nitiride has beenconsidered to be the component of this coating layer. Coating layersformed by PVD or plasma-assisted CVD method are, however, accompanied bysuch drawbacks that they contain cubic boron nitride at low contents anddue to the overall low hardness of the coating layers and the weakbonding between the coating layers and their corresponding substrates,the resultant coated layers cannot be used for actual applications.

In Japanese Provisional patent publication No. 95881/1982, whichdiscloses tools produced in accordance with these conventional methods,coating layers made of cubic boron nitride are formed directly onsurfaces of sintered silicon nitride bodies as substrates. They areproduced by conventional CVD, PVD or plasma-assisted CVD method oralternatively by coating the surfaces with hexagonal boron nitride andthen heat-treating the coating layers of hexagonal boron nitride to formcoating layers consisting of cubic boron nitride. Therefore, theabove-mentioned coated tools are accompanied by such drawbacks that evenif coating layers of cubic boron nitride are formed on the surfaces ofthe substrates, the contents of cubic boron nitride in coating layersare very low or otherwise the adhesion between substrates and theircorresponding coating layers are poor.

SUMMARY OF THE INVENTION

An object of this invention is to solve the above-mentioned problems anddrawbacks, and specifically to provide a cubic boron nitride coatedmaterial having a substrate and dense outer layer of cubic boron nitrideformed and firmly adhered on the substrate by interposing anintermediate layer, which has such properties as inducing orientedgrowth of cubic boron nitride, between the substrate and the outer layerand a producing method thereof.

In one aspect of this invention, there is thus provided a cubic boronnitride coated material including a substrate and an outer layercomposed principally of cubic boron nitride and formed on a surface ofthe substrate, which comprises an intermediate layer formed of at leastone intermediate layer and interposed between the substrate and outerlayer, said intermediate layer or the outermost one of intermediatelayers being formed of a layer of at least one nitrogen-containingcompound selected from the nitrides and nitroxides of Al, Ga, In and Tland mutual solid solutions thereof.

In another aspect of this invention, there is also provided a producingmethod of a cubic boron nitride material by forming, on a surface of asubstrate, an outer layer composed principally of cubic boron nitride,which comprises:

providing, on the surface of the substrate, an intermediate layer formedof at least one intermediate layer, said intermediate layer or theoutermost one of intermediate layers being formed of a layer of at leastone nitrogen-containing compound selected from the nitrides andnitroxides of Al, Ga, In and Tl and mutual solid solutions therof; and

causing the outer layer to undergo oriented growth on a face of thelayer of said at least one nitrogen-containing compound, said face beingdensely packed with nitrogen atoms.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present inventors conducted an investigation on the effects ofconcurrent presence of aluminum nitride to the transformation of varioustypes of boron nitride to cubic boron nitride. As a result, it was foundthat although the activation energy required for the directtransformation of hexagonal boron nitride to cubic boron nitride was 150to 250 kcal/mole, the activation energy required for the transformationof hexagonal boron nitride to cubic boron nitride in the concurrentpresence of aluminum nitride is as low as 40 kcal/mole and theactivation energy required for the transformation of amorphous boronnitride, which had been obtained by thermal decomposition of borazineunder elevated pressure in the concurrent presence of aluminum nitrideand had high activity, to cubic boron nitride was 11 to 20 kcal/mole. Inother words, certain catalytic effects of aluminum nitride were found.Based on such catalytic effects of aluminum nitride, the presentinventors attempted to elucidate the mechanism of transformation ofboron nitride to cubic boron nitride. Neither fusion product norintermediate compound was found to occur between boron nitride andaluminum nitride. It has thus been confirmed that the mechanism offormation of cubic boron nitride in the BN-AlN system is different fromthe dissolution and precipitation mechanism which had conventionallybeen reported with respect to other catalysts. As to the growth of cubicboron nitride on a sintered aluminum nitride body, the (111) face ofcubic boron nitride became extremely predominant as the growth of cubicboron nitride proceeded and no diffusion of aluminum nitride into cubicboron nitride was recognized. From these, it has been found that byusing as a base face the nitrogen-packed crystalline face of aluminumnitride having the wurtzite-type structure, the (111) face of cubicboron nitride, said face being a crystalline face packed densely withnitrogen atoms, is allowed to undergo oriented growth on the base face,leading to completion of this invention.

In the cubic boron nitride coated material according to this invention,cubic boron nitride is formed the outer layer in the form of a dense anduniform, thick or thin film, and the intemediate layer formed of thesingle intermediate layer or the plurality of intermediate layers isinterposed between the outer layer and substrate. The coated materialaccording to this invention has hence excellent adhesion properties andchipping resistance between the outer layer and intermediated layer,between the intermediate layer and the substrate, and where theplurality of intermediate layers are provided, within the intermediatelayers, whereby various superb properties of the outer layer can befully exhibited. For example, the coated material according to thisinvention can be used as a cutting tool or wear resistant tool by makinguse of the high hardness, heat conductivity, wear resistance, oxidationresistance, heat resistance and chemical stability of the outer layer.Further, making use of the high heat conductivity and electricalinsulating property of the outer layer, the coated material according tothis invention can also be used as semiconductor substrate, including anECL or LSI package or a heat sink member for the multichip module of abipolar LSI memory or the mount of a communications semiconductor laser.

When the outer layer is allowed to grow to a thick film, the crystallineface of cubic boron nitride making up the uppermost part of the outerlayer is formed as (111) face substantially in its entirety. As has beenknown very well, this face has the highest hardness and is excellent inwear resistance so that superb advantages have been brought about fromthe view point of its use as cutting tool or wear resistance tool. Inaddition, the outer layer the uppermost surface of which is the (111)face of cubic boron nitride exhibits excellent effects in both heatconductivity and electric insulating property. It can therefore be usedfor parts of various materials by using its isotropic nature.

Coated material according to this invention are therefore useful in theindustry, namely, can be as materials for parts in many industrialfields such as tools, electronic devices, precision instruments androbots. The producing method according to this invention is suitable forthe production of such coated material.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description of theinvention and appended claims.

No particular limitation is imposed on substrates useful in the practiceof this invention, so long as they can withstand producing conditions tobe described subsequently. For example, a variety of metals, alloys,sintered high-speed steels, sintered hard alloys, cermets, ceramics andthe like may be selectively employed depending what end use will bemade.

The outer layer composed principally of cubic boron nitride can beproduced in a form ranging from a thin film on the order of μm to athick film on the order of mm. When it is formed as a layer in the formof a thin film, it is an outer layer made of cubic boron nitride. Whenit is formed as layer in the form of a boron thick film, it may be anouter layer made of cubic nitride or an outer layer made of cubic boronnitride and at least one additional component selected from Fe, Ni, Co,Al and Si, the metal of Groups IVa (Ti, Zr and Hf), Va (V, Nb and Ta)and VIa (Cr, Mo and W) of the Periodic Table, the nitrides and oxides ofAl and Si, and the carbides, nitrides and borides of the metal of GroupsIVa, Va and VIa of the Periodic Table, and their mutual solid solutions.

The intermediate layer interposed between the substrate and outer layermay take various constitutions in accordance with the kind of eachsubstrate to be used or the application or shape of the resultant coatedmaterial according to this invention.

For example, as a first constitution, the intermediate layer may takethe form of a nitrogen-containing compound layer composed of at leastone component selected from the nitrides and nitroxides of Al, Ga, Inand Tl and their mutual solid solutions. Since the layer of thenitrogen-containing compound is interposed between the substrate andouter layer, the excellent properties of the outer layer can be drawnout if the layer of the nitrogen-containing compound is applied to asubstrate having excellent adhesion to the same layer, for example, asubstrate of an AlN base ceramics, Al₂ O₃ base ceramics, Si₃ N₄ baseceramics or the like.

As a second constitution, the intermediate layer may be composed of thenitrogen-containing compound layer and a first adhesion enhancementlayer formed of at least one component selected form the oxides of Al,Ga, In and Tl, the oxides and nitrides of alkaline earh metals, rareearth metals and Si, and mutual solid solutions thereof. In this case,the first adhesion enhancement layer and nitrogen-containing compoundlayer are interposed between the substrate and outer layer in such a waythat the first adhesion enhancement layer is adjacent to the substrateand the nitrogen-containing compound layer is adjacent to the outerlayer. The excellent properties of the outer layer can be drawn out ifthe first adhesion enhancement layer applied to a substrate havingexcellent adhesion to the same layer, for example, a substrate of ZrO₂base ceramics, SiC base ceramics, Si₃ N₄ base ceramics, Al₂ O₃ baseceramics and the like.

As a third constitution, the intermediate layer may be composed of thenitrogen-containing compound layer, the first adhesion enhancementlayer, and a second adhesion enhancement layer formed of at least onecomponent selected from the carbides, nitrides, oxides, borides andsilicides of metals of Groups IVa, Va, and VIa of the Periodic Table andmutual solid solutions thereof. In this case, the second adhesionenhancement layer, first adhesion enhancement layer and nitrogencontaining compound layer are interposed between the substrate and outerlayer in such a way that the second adhesion enhancement layer isadjacent to the substrate, the nitrogen-containing compound layer isadjacent to the outer layer and the first adhesion enhancement layer isinterposed between the second adhesion enhancement layer and thenitrogen-containing compound layer. The excellent properties of theouter layer can be exhibited if the second adhesion enhancement layer isapplied to a substrate having excellent adhesion to the same layer, forexample, to s substrate made of one of various metals or stainlesssteel, one of various alloys including tool steel, a sintered high-speedsteel, a sintered hard alloy, a cermet and the like.

As a fourth constitution, the intermediate layer may be composed of thenitrogen-containing compound layer, the first adhesion enhancementlayer, and a second adhesion enhancement layer composed of at least onecomponent selected from the carbides, nitrides, oxides borides andsilicides of metals of Groups IVa, Va and VIa of the Periodic Table andat least one additional component selected from Fe, Ni, Co, Cr, Mo andW. In this case, the second adhesion enhancement layer, the firstadhesion enhancement layer and nitrogen-containing compound layer areinterposed betweeen the substrate and outer layer is such a way that thesecond adhesion enhancement layer is adjacent to the substrate, thenitrogen-containing compound layer is adjacent to the outer layer andthe first adhesion enhancement layer is interposed between the secondadhesion enhancement layer and the nitrogen-containing compound layer.Since the intermediate layer of the fourth constitution is often formedespecially by the penetration and diffusion of a metal and the like fromthe substrate into the intermediate layer in the course of itspreparation process, the forth constitution is often formed when thesubstrate is made of a sintered hard alloy or cermet.

As other constitutions of the intermediate layer, various constitutionsmay be contemplated such as a constitution having the same constitutionas the above-mentioned third or fourth constitution and an additionallayer of a metal or alloy interposed between the substrate and thesecond adhesion enhancement layer, a constitution composed incombination of the nitrogen-containing compound layer and a layer of atleast one component selected form the carbides, nitrides, oxides,borides and silicides of metals of Groups IVa, Va and VIa of thePeriodic Table and mutual solid solutions thereof.

Among these intermediate layers, the above described first, second,third and fourth constitutions are preferred in view of the adhesionbetween the substrate and the intermediate layer and that between theintermediate layers.

As has been described above, the intermediate layer may be formed into asingle-layered or multi-layered structure. It is, however, the mostimportant feature of this invention that at least the intermediatelayer, which is adjacent to the outer layer, be a nitrogen-containingcompound layer in order to allow cubic nitrogen boride to undergooriented growth. As the nitrogen-containing compound, aluminum nitroxideformed of aluminum nitride and a trace amount of oxygen bonded to thealuminum nitride or a composite nitride or composite nitroxide of Al andGa, In or Tl belonging to Group IVb of the Periodic Table is preferred.Aluminum nitride is, however, most preferred from the stability at hightemperatures and the effectiveness of the catalyst for thetransformation into cubic boron nitride.

The formation of cubic boron nitride on the surface of thenitrogen-containing compound layer is not attributed to the dissolutionand precipitation mechanism but to the direct oriented growth of the(111) face of cubic boron nitride, the nitrogen-packed crystal face, onthe nitrogen-packed crystal face of the nitrogen-containing compoundlayer. It is therefore sufficient if the nitrogen-containing compoundlayer has a thickness enough to have a nitrogen-packed crystal face, forexample, the (001) face in the case of aluminum nitride. Specifically,its thickness may be 0.05 μm or greater, preferably, 0.1 μm or greater.If its thickness is too much on the other hand, the nitrogen-containingcompound layer may be chipped off or damaged. For this reason, thethickness may be 10 μm or less, preferabley, 5 μm or less.

Besides the nitrogen-containing compound layer, the intermediate layermay also contain other layers such as the first and second adhesionenhancement layers which serve to enhance the adhesion between thesubstrate and nitrogen-containing compound layer. In this case, theoverall thickness of the intermediate layer may be 0.05 μm to 15 μm,preferably, 0.1 μm to 10 μm in view of the intermediate layer chippingresistance and strength of the intermediate layer itself.

As specific examples of these intermediate layers, there may bementioned layers of AlN, GaN, InN, TlN, Al(N,O), Ga(N,O), (Al,Ga)N, (Al,In)N, (Al,Tl)N, (Al,Ga)(N,O) and the like as nitrogen-containingcompound layers; and layers of Al₂ O₃, Ga₂ O₃, In₂ O₃, Tl₂ O₃, CaO, SrO,BaO, RaO, BeO, MgO, Sc₂ O₃, Y₂ O₃, La₂ O₃, CeO₂, Ce₂ O₃, Nd₂ O₃, Sm₂ O₃,PrO₂, Gd₂ O₃, Dy₂ O₃, Eu₂ O₃, SiO₂, Ca₃ N₂, Sr₃ N₂, Ba₃ N₂, Ra₃ N₂, Be₃N₂, Mg₃ N₂, ScN, YN, LaN, CeN, Si₃ N₄, (Si,Al)(O,N), (Al,Y)₂ O₃ and thelike as first adhesion enhancement layers. Illustrative of the secondadhesion enhancement layer composed of at least one component selectedfrom the carbides, nitrides, oxides, borides and silicides of metals ofGroups IVa, Va and VIa of the Periodic Table and mutual solid solutionsthereof, may be mentioned layers of TiC, ZrC, HfC, VC, TaC, NbC, Cr₃ C₂,Cr₇ C₃, Mo₂ C, WC, TiN, ZrN, VN, TaN, CrN, TiO, TiO₂, ZrO₂, Ta₂ O₅, WO₃,TiB₂, VB₂, TaB₂, TiSi₂, TaSi₂, Ti(N,C), (Ti,Ta)C, (Ti,W)C, Ti(N,O),Ti(C,N,O), (Ti,Ta,W)C and the like. These intermediate layers may bemade not only as stoichiometric compounds but also non-stoichiometriccompounds. These non-stoichiometric compounds may also be formed assubstoichiometric compounds in each of which the ratio of non-metallicelement(s) to metallic element(s) is small.

In the present invention, the above-mentioned cubic boron nitridematerial is prepared by the following manner. Namely, an inner layercomposed of a single intermediate layer or a plurality of intermediatelayer and an outer layer made principally of cubic boron nitride areprovided on a surface of a substrate. The intermediate layer isinterposed between the substrate and outer layer. The singleintermediate layer or the outermost one of the plurality of intermediatelayers is a layer of at least one nitrogen-containing compound selectedfrom the nitrides and nitroxides of Al, Ga, In and Tl and mutual solidsolutions thereof. The outer layer is formed through its oriented growthon a face of the layer of said at least one nitrogen-containingcompound, said face being densely packed with nitrogen atoms. Theformation of the outer layer through its oriented growth on thenitrogen-packed face of the nitrogen-containing compound layer may beeffected in various ways. In particular, it is most preferable toconduct it under high-pressure and high-temperature conditions, underwhich cubic boron nitride is stable, from the viewpoint of accelerationof the oriented growth of cubic boron nitride. Preferably, theseconditions include as pressure of 4.5 GPa or higher and a temperature of700° C. or higher.

Illustrative substrates useful in the method of this invention for theproduction of cubic boron nitride coated materials may include metals,alloys, sintered hard alloys, cermets and ceramics, which can withstandthe above-mentioned high-pressure and high-temperature conditions.Plates, ingots, powders and green compacts may be used as startingmaterials for these substrates. When plates or ingots are used asstarting materials, it is preferable to subject a surface of eachsubstrate to a nitriding or carburizing treatment or to polish, wash anddry the surface of the substrate as needed because its adhesionproperties to the corresponding intermediate layer can be improved.

The intermediate layer may be provided on the surface of thecorresponding substrate in various ways. When the nitrogen-containingcompound layer, the first adhesion enhancement layer and the secondadhesion enhancement layer composed of at least one component selectedfrom the carbides, nitrides, oxides, borides and silicides of metals ofGroups IVa, Va and VIa of the Periodic Table and mutual solid solutionthereof are provided by way of example, they may be formed as layers inthe form of thin films by a CVD, PVD or plasma-assisted CVD method.Alternatively, after vacuum-deposition of metals, they may be convertedto layers of metal compounds by carburizing and/or nitriding treatments.As another alternative, they may be sprayed or brushed in powdery forms.As a further alternative, they may also be provided in the form of greencompacts by dry pressing. As a still further alternative, they may alsobe provided in the form of plates.

When it is required to provide a layer of a metal or alloy as anintermediate layer on a surface of a substrate in order to enhance theadhesion of its associated outer layer to the surface of the substrate,the layer of the metal or alloy may be formed by deposition besides PVDmethod such as vacuum evaporation, ion plating or sputtering.

Starting materials useful for the formation of outer layers may includeamorphous boron nitride, hexagonal boron nitride, rhombohedral boronnitride and wurtzite-type boron nitride as well as their mixtures withcubic boron nitride. When cubic boron nitride is present in a startingmaterial provided for the formation of an outer layer, the cubic boronnitride accelerates the transformation of the starting material intocubic boron nitride. Inclusion of cubic boron nitride is thereforepreferred for the formation of an outer layer. Needless to say, cubicboron nitride can be used, as is, for the formation of an outer layer.In addition, amorphous boron nitride which can be obtained by thethermal decomposition of borazine or a derivative thereof under pressureand contains hydrogen is preferred as a starting material for theformation of an outer layer since the activation energy required for itstransformation to cubic boron nitride is low. Further, a mixture orhexagonal boron nitride, amorphous boron nitride or hydrogen-containingamorphous boron nitride and at least one material selected fromborazine, borazine derivatives and materials containing boron, nitrogenand hydrogen and capable of yielding boron nitride is preferred as astarting material for the formation of an outer layer because the lattercomponent facilitates the transformation of the former component intocubic boron nitride.

The term "borazine" as used herein means a compound having as chemicalformula, B₃ N₃ H₆. On the other hand, the term "borazine derivatives"indicates boron-nitrogen-hydrogen compounds of 6-membered ringstructures such as 2,4-diaminoborazine (B₃ N₅ H₈, borazonaphthalene (B₅N₅ H₈) and borazobiphenyl (B₆ N₆ H₁₀) by way of example. By the term"materials containing boron, nitrogen and hydrogen and capable ofyielding boron nitride" are meant, for example, those formed of boronhydride and ammonia or hydrazine such as diborane (B₂ H₆), tetraborane(B₄ H₁₀), pentaborane-9 (B₅ H₉), octaborane-12 (B₈ H₁₂) and decaborane(B₁₀ H₁₄).

Among borazine, borazine derivatives and materials containing boron,nitrogen and hydrogen and capable of yielding boron nitride, those beingliquid at room temperature such as borazine, 2,4-diamino-borane,pentaborane-9, pentaborane-11 and hexaborane-12 are preferred asstarting materials for the formation of outer layers because thetransformation of powder or a green compacts of hexagonal boron nitride,amorphous boron nitride or hydrogen-containing amorphous boron nitrideinto cubic boron nitride is facilitated when it is wet with such liquidstarting materials.

As a starting materials useful in the formation of an outer layer, it ispossible to incorporate at least one of Fe, Ni, Co, Al, Si and metals ofGroup IVa, Va and VIa of the Periodic Table, the carbides, nitrides andborides of metal of Groups IVa, Va and VIa of the Periodic Table andmutual solid solutions thereof in a material which can be transformedinto cubic boron nitrides, such as that mentioned above.

The producing method according to this invention for the production of acubic boron nitride material is now specifically described. In a firstmethod, when a substrate as a starting material is, for example, a plateor ingot made of a drawn product, rolled product, cast product, forgedproduct or sintered product, an intermediate layer is provided by CVD,PVD or plasma-assisted CVD method after polishing, washing and drying asurface of the substrate. Thereafter, in order to form an outer layer inthe form of a thin layer on the order of 0.05 μm to 20 μm for example, astarting material adapted to form an outer layer by CVD, PVD orplasma-assisted CVD method is provided on the surface of theintermediate layer. The substrate with the intermediate layer and thestarting material for the outer layer is then place in a belt-type orgirdle-type high-pressure and high-temperature apparatus, in which thestarting material is treated under high-pressure and high-temperatureconditions under which cubic boron nitride is stable.

In a second method, a substrate similar to that employed in the firstmethod is used as a starting material. After forming an intermediatelayer on a surface of the substrate in the same manner as the firstmethod, a starting material adapted to form an outer layer is providedin the form of powder or a green compact on the surface of theintermediate layer in order to form the outer layer in the form of athick film, for example, on the order of about 0.1 mm to 0.8 mm. Thesubstrate with the intermediate layer and the starting material for theouter layer is then placed in a high-pressure and high-temperatureapparatus, in which the starting material is treated under high-pressureand high-temperature conditions under which cubic boron nitride isstable.

In a third method, a substrate similar to that employed in the firstmethod is used as a starting material. After forming an intermediatelayer in the form of powder, as green compact or a plate on a surface ofthe substrate, a starting material adapted to form an outer layer isprovided in the form of powder or a green compact on the surface of theintermediate layer. The substrate with the intermediate layer and thestarting material for the outer layer is then placed in a high-pressureand high-temperature apparatus, in which the starting material istreated under high-pressure and high-temperature conditions under whichcubic boron nitride is stable.

In a fourth method, starting materials adapted to form a substrate,intermediate layer and outer layer are all provided in the form ofpowders and/or green compacts. They are thereafter placed in ahigh-pressure and high-temperature apparatus, in which the startingmaterials are treated under high-pressure and high-temperatureconditions under which cubic boron nitride is stable.

In the above description, the oriented growth of each outer layer wasconducted under high-pressure and high-temperature conditions underwhich cubic boron nitride is stable. The oriented growth of an outerlayer can however be effected by conventional PVD or plasma-assisted CVDmethod. Among the above-mentioned methods, the first or second method ispreferred when an outer layer of particularly dense cubic boron nitrideis desired or the strength of an intermediate layer is important.

The cubic boron nitride coated material according to this invention iscoated material including a coating layer, which is composed of anintermediate layer and an outer layer, formed on a surface of asubstrate. On the nitrogen-packed face of a nitrogen-containing compoundlayer as the intermediate layer, the nitrogen-packed face of cubic boronnitride has been allowed to undergo oriented growth as the outer layer.Accordingly, the outer layer contains cubic boron nitride at a highdensity and has properties similar to various good properties as highhardness, high heat conductivity and high electrical insulating propertywhich cubic boron nitride has inherently. Since the outer layer has beenformed by its oriented growth on the nitrogen-packed face of thenitrogen-containing compound layer as the intermediate layer, the outerlayer has excellent adhesion property with the intermediate layer. Sincethis intermediate layer may be formed with a material suitable for thetype of each substrate and into a constitution suitable for the type ofeach substrate, it has excellent adhesion property with the substrate.For the reasons mentioned above, the cubic boron nitride coated materialaccording to this invention can fully exhibit the excellent propertiesof its outer layer.

Having generally described the invention, a more complete understandingcan be obtained by reference to certain specific examples, which areprovided herein for purposes of illustration only and are not intendedto be limiting unless otherwise specified.

EXAMPLES EXAMPLE 1

After polishing the surface of a substrate formed of a sintered ceramicbody, the composition of which was Al₂ O₃ - 20 vol.% Ti(N,C) - 0.5 vol.%MgO, and having dimensions of 10 mm across and 3 mm thick by means of asdiamond grinding wheel, the substrate was washed with distilled waterand ethyl alcohol and then dried. The substrate was then placed in thereactor of a CVD apparatus and held for 20 minutes at a pressure of 70Torr and temperature of 1,050° C. in an atmosphere consisting of 5 vol.%AlCl₃ - 35 vol.% N₂ - 60 vol.% H₂ to form an AlN layer on the surface ofthe substrate. After evacuation of the gas from the reactor, thesubstrate was held for 120 minutes at a temperature of 50 Torr and atemperature of 1,000° C. in an atmosphere of 9 vol.% BCl₃ - 23 vol.%H₂ - 36 vol.% NH₃ - 32 vol.% Ar, thereby forming a layer of boronnitride on the surface of the AlN layer. At this stage, the layer ofboron nitride was investigated by X-ray diffraction. As a result, it wasfound to be a mixture of amorphous boron nitride and hexagonal boronnitride. The substrate with both AlN layers was then placed in ahigh-pressure and high-temperature apparatus, in which they were treatedat a pressure of 5.5 GPa and a temperature of 1,300° C. to obtain acoated material of this invention. The thus-obtained coated materialaccording to this invention was investigated by X-ray diffraction and ascanning electron microscope. The outer layer was 2 μm thick layer ofcubic boron nitride while the intermediate layer was 0.5 μm thick Allayer. The outer layer was a dense and uniform thin layer and itshardness was 5,300 kg/mm₂ in terms of micro-Vickers hardness.

EXAMPLE 2

After machining and treating the surface of a substrate formed of asintered ceramic body the composition of which was ZrO₂ - 5 vol.% MgO,and having dimensions of 10 mm across and 3 mm thick in the same manneras in Example 1, the substrate was placed in the reactor of a CVDapparatus. The substrate was held for 120 minutes at a pressure of 30Torr and a temperature of 1,100° C. in an atmosphere of 5 vol.% AlCl₃ -10 vol.% CO - 10 vol.% CO₂ - 75 vol.% H₂, therby forming an Al₂ O₃ layeron the surface of the substrate. After evacuating the gas from thereactor, an AlN layer was formed on the surface of the Al₂ O₃ layerunder the same conditions as in Example 1. After evacuating the gasagain from the reactor, as layer of boron nitride was formed on thesurface of the Al layer under the same conditions as in Example 1. Thesubstrate with the Al₂ O₃, AlN and boron nitride layers was placed in ahigh-pressure and high-temperature and processed in the same manner asin Example 1, thereby obtaining a coated material according to thisinvention. The resultant coated material according to this invention wasinvestigated by X-ray diffraction and a scanning electron microscope.The outer layer was found to be a 2 μm thick layer of cubic boronnitride whereas the intermediate layer was found to consist of an AlNlayer of 0.5 μm thick and an Al₂ O₃ layer of 0.5 μm thick. On the otherhand, the outer layer was a dense and uniform, thin film and itshardness was 5,300 kg/mm² in terms of micro-Vickers hardness.

EXAMPLE 3

After machining and treating the surface of a substrate made of asintered hard alloy, the composition of which was WC - 10 vol.% Co, andhaving dimensions of 10 mm across and 3 mm thick in the same manner asin Example 1, the substrate was placed in the reactor of a CVDapparatus. The substrate was held for 30 minutes at a pressure of 20Torr and a temperature of 1,000° C. in an atmosphere of 8 vol.% TiC₄ - 5vol.% CH₄ - 87 vol.% H₂, thereby forming a TiC layer on the surface ofthe substrate. Thereafter, the substrate and TiC layer were treatedthrough the same steps under the same conditions as in Example 2 toobtain a coated material according to this invention. The resultantcoated material according to this invention was investigated by X-raydiffraction and a scanning electron microscope. The outer layer wasfound to be a 2 μm thick layer of cubic boron nitride whereas theintermediate layer was found to consist of an AlN layer of 0.5 μm thickan Al₂ O₃ layer of 0.5 μm thick and a TiC layer of 0.5 μm. On the otherhand, the outer layer was a dense and uniform, thin film and itshardness was 5,300 kg/mm² in terms of micro-Vickers hardness.

EXAMPLE 4

After machining and treating the surface of a substrate made of sinteredceramic body, the composition of which was Si₃ N₄ - 8 vol.% AlN - 8vol.% MgO, and having dimensions of 10 mm across and 3 mm thick in thesame manner as in Example 1, an AlN layer was formed on the surface inthe same manner as in Example 1. After providing on the surface of theAlN layer as green compact of nitrogen-containing amorphous boronnitride obtained by thermally decomposing borazine under pressure, thesubstrate with the green compact was placed in a high-pressure andhigh-temperature apparatus, in which they were treated at a pressure of6 GPa and a temperature of 1,400° C. to obtain a coated materialaccording to this invention. The resultant coated material acoording tothis invention was investigated by X-ray diffraction and a scanningelectron microscope. The outer layer was found to be a 0.4 mm thicklayer of cubic boron nitride whereas the intermediate layer was found toconsist of an AlN layer of 0.5 μm thick. On the other hand, the outerlayer was a dense and uniform, thick film and its hardness was 5,700kg/mm² in terms of micro-Vickers hardness.

EXAMPLE 5

On the surface of substrate made of a sintered ceramic body, thecomposition of which was TiC - 10 vol.% NbC - 10 vol.% VC, and havingdimensions of 10 mm across and 3 mm thick, an Al₂ O₃ layer and AlN layerwere formed in the same manner as in Example 2. After providing a greencompact of amorphous boron nitride on the surface of the AlN layer, thesubstrate with the Al₂ O₃ and AlN layers and green compact was placed ina high-pressure and high-temperature apparatus, in which they weretreated at a pressure of 6 GPa and a temperature of 1,500°C. to obtain acoated material according to this invention. The resultant coatedproduct according to this invention was investigated by X-raydiffraction and a scanning electron microscope. The outer layer wasfound to be a 0.2 mm thick layer of cubic boron nitride whereas thatintermediate layer was found to consist of an AlN layer of 0.5 μm thickand an Al₂ O₃ layer of 0.5 μm thick. On the other hand, the outer layerwas a dense and uniform, thick film and its hardness was 5,500 kg/mm² interms of micro-Vickers hardness.

EXAMPLE 6

On the surface of a substrate formed of a sintered cermet alloy, thecomposition of which was TiC - 5 vol.% TiN - 2 vol.% WC - 6 vol.% Mo₂C - 10 vol.% Ni, and having dimensions of 10 mm across and 3 mm thick aTiC layer, Al₂ O₃ layer and AlN layer were formed in order in the samemanner as in Example 3. After providing a green compact of hexagonalboron nitride on the surface of the AlN layer, the substrate with theTiC, Al₂ O₃ and AlN layers and the green compact was placed in ahigh-pressure and high-temperature apparatus, in which they were treatedat 6.5 GPa and 1,600° C. to obtain a coated material according to thisinvention. The resultant coated material according to this invention wasinvestigated by X-ray diffraction and a scanning electron microscope.The outer layer was found to be a 0.6 mm thick layer of cubic boronnitride whereas the intermediate layer was found to consist of an AlNlayer of 0.5 μm thick, an Al₂ O₃ layer of 0.5 μm thick and a TiC-Nilayer of 0.5 μm. On the other hand, the outer layer was a dense anduniform, thick film, and its hardness was 5,600 kg/mm² in terms ofmicro-Vickers hardness, a specific resistance was 1.3×10⁻¹⁰ Ω-cm, andits dielectric constant was 8.3 as measured under and 10 KHg.

EXAMPLE 7

A mixed powder having a composition of WC - 20 vol.% TiC - 7 vol.% TaC -11 vol.% Co was placed in a mold, in which the mixed powder was pressed.Thereafter, Ti(C,N) powder, Y₂ O₃ powder and AlN powder were sprinkledone after another in order with pressing after each sprinkling. Theresultant green compact was then placed in a high-pressure andhigh-temperature apparatus, in which it was treated at a pressure of 6.0GPa and a temperature of 1,450° C. to obtain a coated material accordingto this invention. The resultant coated material acoording to thisinvention was investigated by X-ray diffraction and a scanning electronmicroscope. The outer layer was found to be a 0.5 mm thick layer ofcubic boron nitride whereas the intermediate layer was found to consistof an Al(N₀.99,O₀.01) layer of 0.3 mm thick, a Y₂ O₃ layer of 0.2 mmthick and a Ti(C,N)-Co layer of 0.3 mm. On the other hand, the outerlayer was a dense and uniform, thick film, and its hardness was 5,400kg/mm² in terms of micro-Vickers hardness.

EXAMPLE 8

After rapping, cleaning and drying the surface of a substrate having acomposition equivalent to "Inconel 713c" (trade name) and dimensions of10 mm×10 mm ×1 mm, it was placed in the reactor of an ion platingapparatus. After evacuating the interior of the reactor, the reactor washeated to 500° C. at which Ar bombardment was carried out at 0.2 Torrfor 10 minutes. Thereafter, a Ti ingot was caused to evaporate into Tiions by an electron beam gun under 6 KV and 0.4 A and C₂ H₂ wasintroduced as reactant gas to a pressure of 5×10⁻⁴ Torr. By applying anegative bias voltage of 100 V to the substrate, vacuum evaporation wasconducted for 20 minutes. After evacuating the interior of the reactor,O₂ was introduced as a reactant gas to a pressure of 9×10⁻⁴ Torr and anAl ingot was caused to evaporate into ions by an electron beam gun under3 KV and 0.3 A. By applying a negative bias voltage of 20 V to thesubstrate, vacuum evaporation was conducted for 15 minutes. Subsequentto evacuation of the interior of the reactor, N² was introduced as areactant gas to a pressure of 5×10⁻⁴ Torr and an Al ingot was caused toevaporate into ions to conduct vacuum evaporation. A green compact ofnitrogen-containing amorphous boron nitride, which had been obtained bythermal decomposition of borazine under pressure, was provided on thesurface of the vacuum-deposited layer. The substrate with the greencompact was placed in a high-pressure and high-temperature apparatus, inwhich the green compact was wet with borazine to eliminate voids.Thereafter, it was treated at a pressure of 6 GPa and a temperature of1,000° C. to obtain a coated material according to this invention. Theresultant coated material according to this invention was investigatedby X-ray diffraction and a scanning electron microscope. The outer layerwas found to be a 0.3 mm thick layer of cubic boron nitride whereas theintermediate layer was found to consist of an AlN layer of 1.0 μm thick,an Al₂ O₃ layer of 0.5 μm thick and a TiC layer of 10. μm. On the otherhand, the outer layer was a dense and uniform, thick film, and itshardness was 5,000 kg/mm² in terms of micro-Vickers hardness.

EXAMPLE 9

After cleaning an drying the surface of a substrate made of a Mo platehaving dimensions of 10 mm×10 mm×1 mm, the substrate was placed in thereactor of a CVD apparatus. It was then treated for 40 minutes at apressure of 50 Torr and a temperature of 900° C. in an atmosphere of 8vol.% TiCl₄ - 45 vol.% N₂ - 47 vol.% H₂, thereby forming as TiN layer onthe surface of the substrate. After evacuation of the interior of thereactor, the substrate and TiN layer was treated for 180 minutes at apressure of 70 Torr and a temperature of 900° C. in an atmosphere of 5vol.% AlCl₃ - 5 vol.% CO - 5 vol.% CO₂ - 85 vol.% H₂ so that an Al₂ O₃layer was formed on the surface of the TiN layer. After evacuation ofthe interior of the reactor, the substrate with the TiN and Al₂ O₃layers was treated for 40 minutes at a pressure of 70 Torr and atemperature of 900° C. in an atmosphere of 8 vol.% AlCl₃ - 35 vol.% N₂ -57 vol.% H₂ to form an A layer on the surface of the Al₂ O₃ layerSubsequent to evacuation of the interior of the reactor, the thustreated substrate was treated for 180 minutes at a pressure of 100 Torrand a temperature of 600 °0 C. in an atmosphere of 5 vol.% B₃ N₃ H₆ - 35vol.% N₂ - 60 vol.% H₂. Thereafter, the resultant substrate was placedin the high-temperature apparatus, in which it was treated at a pressureof 6 GPa and a temperature of 1,400° C. to obtain a coated materialaccording to this invention. The resultant coated material according tothis invention was investigated by X-ray diffraction and a scanningelectron microscope. The outer layer was found to be a 0.2 μm thicklayer of cubic boron nitride whereas the intermediate layer was found toconsist of an AlN layer of 1.0 μm thick, an Al₂ O₃ layer of 0.5 μm thickand a TiN layer of 1.0 μm. On the other hand, the outer layer was adense and uniform, thick film, and its hardness was 5,400 kg/mm² interms of micro-Vickers hardness.

EXAMPLE 10

On the surface of a substrate formed of a sintered hard alloy having acomposition of WC - 10 vol.% Co and dimensions of 10 mm across and 5 mmthick, there were provided, in order, a Ti(C,N) green compact, an Si₃N₄ - A_(l2) O₃ green compact on the surface of the Ti(C,N) greencompact, an AlN green compact on the surface of the Si₃ N₄ -Al₂ O₃ greencompact, and a green compact of 10 vol. % TiN - 3 vol.% WC - 2 vol.%Ni - 30 vol.% cubic BN - 55 vol.% amorphous BN. The substrate with thegreen compacts was placed in a high-pressure and high-temperatureapparatus, in which they were treated at a pressure of 6 GPa and atemperature of 1,450° C. to obtain a coated material according to thisinvention. The resultant coated material according to this invention wasinvestigated by X-ray diffraction and a scanning electron microscope.The outer layer was found to be a 0.4 mm thick layer made principally ofcubic boron nitrides whereas the intermediate layer was found to consistof an Al(N₀.99,O₀.01) layer of 0.2 mm thick, an (Si,Al)(N,O) layer of0.2 mm thick, and a Ti(C,N)-Co layer of 0.2 mm thick. The hardness ofthe outer layer was 4,300 kg/mm² in terms of micro-Vickers hardness.

Having now fully described the invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade thereto without departing from the spirit or scope of the inventionas set forth herein.

We claim:
 1. A method for producing a cubic boron nitride coatedmaterial by forming, on a surface of a substrate, an outer layerconsisting essentially of cubic boron nitride, whichcomprises:providing, on the surface of the substrate, at least oneintermediate layer comprising at least one nitrogen-containing compoundselected from the group consisting of nitrides and nitroxides of Al, Ga,In and Tl and mutual solid solutions of the aforesaid nitrides andnitroxides; and causing the outer layer to undergo oriented growth on aface of the intermediate layer, said face being densely packed withnitrogen atoms.
 2. A method according to claim 1, wherein the orientedgrowth of the outer layer is effected under high pressure andtemperature conditions under which cubic boron nitride is stable.
 3. Amethod according to claim 2, wherein the high pressure and temperatureconditions, under which cubic boron nitride is stable, include apressure of 4.5 GPa or higher and a temperature of 700° C. or higher. 4.A method according to claim 1, wherein the oriented growth of the outerlayer is effected by a physical vapor deposition method or a plasmachemical vapor deposition method.
 5. A method according to claim 1,wherein said oriented growth is such that the outer layer, in itsoutermost portion, presents a crystalline face that lies substantiallyin a (111) plane.
 6. A method according to claim 1, wherein said face ofthe intermediate layer is a (001) crystal face.